In an effort to better understand how these changes fit into the evolution of the Regimental System, I just read
Where Did That Regiment Go? by Gerry Murphy; all in all, a solid reference book - the narrative has a few nuggets with regards to dates and times, but the real value is the charts showing the evolution of Regimental identities for the Infantry and Cavalry corps.
For my own good, I wrote out some notes that I copied here that can be considered the Regimental System 101:
1. The Regimental system as we understand it has its origins in the beginning of the English/British Army in the late 1600s; this is where roots of the more senior regiments lie. However, the formal birth of the British (and thus by extension, Canadian) Regimental system was in the Royal Warrants of 1743, 1747 and 1751 which formalized the system of colours, standardized uniforms and numbered Regiments organized on seniority;
2. The "Growth Period" of the regimental system was from the Restoration period in the late 1600s to the post Napoleonic period and saw the growth of the Line Infantry Regiments of Foot to 100 Regiments (1-99th of Foot and the Rifle Brigade). Note that this did not include the three Regiments of Guards (Grenadier, Coldstream, and Scots). This period was filled with fits and starts (some regiments were stood up, disbanded, stood up again, etc) with the primary growth spurts occurring during the 7 Years War and the Napoleonic Wars. A final growth period occurred in 1862 when the East India Company regiments were absorbed.
3. By the middle of Victorian Britain, the pre-Cardwell/Childers British Infantry system consisted of the Guards regiments and 141 Battalions belonging to to 110 Infantry Regiments of Foot; the 1st-25th each had 2 Battalions, while the 26th-109th had 1 each except the 60th (4) and the 79th (1). The Rifle Brigade had 4 battalions. Cardwell/Childers in 1881 - which can be considered the "first shock" to the 250 year old system - moved the focus from "numbered" identity" to a "named" identity. As well, all battalions above the 25th were paired (except for the 60th, 79th and Rifle Bde). Cardwell/Childers meant the Regimental System moved from 110 Line Regiments to 69 plus the 3 Regiments of Guards (this was purely an organizational change - the number of battalions remained constant).
4. There were obviously big expansions and contractions through the World Wars, but the Regimental System remained largely untouched (Regiments just grew in battalions - the Northumberland Fusiliers had 51 battalions during the First World War). By the end of the Second World War, all the excess Battalions of most regiments were disbanded (along with almost all Irish Regiments), leaving 64 single battalion Regiments of the Line, the five Guards Regiments of 8 battalions, the four Gurkha Regiments of 8 battalions and the Parachute Regiment of 3 battalions for an Infantry Corps of 74 Regiments of 83 battalions. The "Regimental Army" was still very similar to that of the Cardwell/Childers Army. With the British Empire dying a slow death after the Second World War, the Regimental System went through 4 additional periods of "shock":
4.a. The second shock was during the post India/Suez phase from 1957-1962. By the end of it, 16 mergers had occurred dropping the number of line Regiments to 49. The Guards, Gurkhas and Paras remained the same for an Infantry Corps of 59 Regiments of 68 battalions.
4.b. The third shock was during the shift from Empire to NATO from 1962-1970. The big change here was the move towards "Big Regiments"; the Line Regiments dropped only 10 battalions but, through mergers, saw the number of Regiments drop to 28. With 3 Gurkha battalions also folded up, the Infantry Corps consisted of 38 Regiments of 55 battalions.
4.c. The fourth shock was the post Cold War "Options for Change" from 1991-1994. Due to mergers and amalgamations, the Line Regiments dropped to 25 Regiments of 30 battalions. Three Regiments of Gurkhas disappeared and a single Gurkha Regiment of 2 battalions remained. The Guards Regiments were untouched, but 3 battalions were axed for an Infantry Corps of 32 Regiments of 40 Battalions.
4.d. The fifth shock stemmed from the 2004 White Paper. This made another significant "Big Regiments" move and by 2007, the Line Regiments only lost 3 battalions but had, through mergers, dropped to 10 Regiments. The Guards, Gurkhas and Paras were left alone (although a Para bn was cut to the SOF) for an Infantry Corps of 17 Regiments of 37 battalions.
So, to sum up, the Regimental System in Britain grew with the growth of the Empire to 110 Regiments (plus Guards). The first shock of Cardwell/Childers was significant, but it created the Regimental System we are most familiar with (i.e. it created the "Royal Buckshot Fusiliers"). The third and fifth shocks were also significant as they pushed for big, multi-battalion regiments.
This Army 2020 plan represents a sixth shock, or, more likely, the final part to the fifth shock started in 2004, but it seems to be quite small to the Regimental System. It will see the loss of 5 battalions, but no actual Regiments. However, it will leave a couple single battalion regiments which, historically, have been the target for further amalgamation. At this point, the Royal Regiment of Fusiliers and the Royal Welsh Regiment may be living on borrowed time (along with some of the 2 battalion Regiments).
The so what of this? The Guards Regiments are protected, with the Grenadier, Coldstream and Scots Guards having 300+ years of unbroken, unmerged service (and the Welsh and Irish Guards having 100+ years). These will likely be the last Regiments to go.
As well, the Regimental System has never, since 1881, been a stable and monolithic institution - it has been in a constant state of flux. Even before 1881 it was constantly changing (although constantly growing instead of constantly shrinking). Any claims for "centuries old Regiments" is technically incorrect - the last 2 "pure" Regiments with single, non-amalgamated lineages were folded up in 2007. Today, the current British Regiments hold the lineage of numerous numbered Regiments from the hey-day of the Empire; the 5 battalions of the The Rifles have 21 antecedent Regiments, with the 1st Battalion The Rifles having lineage to 9 Regiments (the 11th, 28th, 39th, 49th, 54th, 61st, 62nd, 66th, and 99th Regiments of Foot). Historic regiments that have been folded up in the past were actually not that old - the Royal Green Jackets existed from 1958 to 2007.
Finally, the Regimental System through "Growth" (200 years) and "Shocks" (150 years) has evolved to the changing requirements of Army. There is a lot of gnashing of teeth as silverware is transferred from one mess to another, but the Army goes on, new traditions are made and new battle honours won, and the world carries on. We should never let Regimental mafias drive organizational agendas as their claims to operational relevance or the health of the Army are empty and not historically supported.
The book also covers the cavalry, which although a little more convoluted due to naming conventions (Dragoons, Hussars, Guards, Lancers, etc) has the same themes. Of note, the cavalry have attempted to keep their numbered regimental affiliation until the current day; with the merging of the 9th/12th Royal Lancers with the Queen's Royal Lancers, the 1st Queen's Dragoon Guards will be the last Regiment in the British Army to hold its original numbered designation.
Canada's system, with its own unique quirks and features, would be useful.